Electrophotographic liquid developing apparatus

ABSTRACT

An electrophotographic developing apparatus employing a liquid developer for developing an electrostatic latent image on an insulating sheet, the apparatus comprising (1) at least two pairs of nip rollers, each pair comprising a first roller disposed on one side of the insulating sheet and a second roller disposed adjacent the first roller and on the opposite side of the insulating sheet where the rollers nip and transport the insulating sheet and where successive pairs of rollers are disposed along the direction of movement of the sheet, (2) at least one pair of endless belts suspended between selected nip rollers at the end portions thereof, the selected rollers being disposed along the direction of movement of the insulating sheet, (3) a plurality of development electrode rollers disposed between each adjacent pair of first rollers and on the same side of the insulating sheet as each of the first rollers and having smaller diameters than the nip rollers with their end portions disposed on the endless belts, and (4) means for supplying the developer liquid onto the surface of the sheet bearing the electrostatic latent image.

Fukushima et al.

[451 Aug. 21, 1973 1 ELECTROPHOTOGRAPHIC LIQUID DEVELOPING APPARATUS [75] Inventors: Osamu Fukushima; Masamichi Sato,

both of Asaka, Saitama, Japan [73] Assignee: Fuji Photo Film Co., Ltd., Minami Ashigara-Shi Kanagawa, Japan [22] Filed: June 22, 1971 [211 Appl. No.: 155,510

[30] Foreign Application Priority Data June 22, 1970 Japan 45/54208 [52] US. Cl 118/637, 117/37 LE, 118/D1G. 23, t 355/10, 95/89 L [51] int. G03g13/00 [58] Field of Search 118/637, DIG. 23; 117/37 LE; 96/1 L; 355/10 [5 6] References Cited UNITED STATES PATENTS 3,308,737 3/1967 Susumu Fukuda 95/89 3,328,193 6/1967 Oliphant etal..... 117/37 3,556,050 l/197l Trachtenberg 118/637 3,448,720 6/1969 Graham 118/109 1,819,848 8/1931 Simjia'n 118/637 L X 3,592,678 7/1971 Honjo et a1. 117/37 Primary Examiner-Mervin Stein Assistant Examiner-Leo Millstein Attorney-Gerald J. Ferguson, Jr.

[57] ABSTRACT An electrophotographic developing apparatus employing a liquid developer for developing an electrostatic latent image on an insulating sheet, the apparatus comprising (1) at least two pairs of nip rollers, each pair comprising a first roller disposed on one side of the insulating sheet and a second roller disposed adjacent the first roller and on the opposite side of the insulating sheet where the rollers nip and transport the insulating sheet and where successive pairs of rollers are disposed along the direction of movement of the sheet, (2) at least one pair of endless belts suspended between selected nip'rollers at the end portions thereof, the selected rollers being disposed along the direction of movement of the insulating sheet, (3) a plurality of development electrode rollers disposed between each adjacent pair of first rollers and on the same side of the insulating sheet as each of the first rollers and having smaller diameters than the nip rollers with their end portions disposed on the endless belts, and (4) means for supplying the developer liquid onto the surface of the sheet bearing the electrostatic latent image.

20 Claims, 10 Drawing Figures Patented Aug. 21,1973 3,753,419

2 Shuts-Sheet 1 FIG. 3

FIG.4

INVENTORS OSAMU FUKUSHIMA MASAMICHI SATO ATTORNEYS Pa.-tented-Aug. 21,1973 3,753,413

2 Shuts-Shut 2 os 'Mu FUKUSHIMA MASAMICHI SATO BY gym ,5 25221..

ATTORNEYS.

ELECTROI'IIGTOGRAPI-IIC LIQUID DEVELOPING APPARATUS trostatic image is nipped and carried between rollers,

and liquid developer is fed onto the electrostatic image surface. FIG. 1 is a typical example of such conventional devices which is provided with multiple nip rollers and with a means supply a developer liquid. The important features of such device reside in the fact that the many electrode rollers directly contact with the developed surface and that the upper or lower roller in every nip roller pair if forced to rotate.

The inventors have found that such device is not suited in some aspects for the reproduction of high quality images and have invented improved devices overcoming the defects accompanied by the conventional ones.

Considering the surface smoothness or roughness an electrophotographic sheet as for a faithful reproduction of continuous tone images, it is quite rational that the surface roughness should be as small as possible.

However, when a conductive electrode roller is brought into contact with such surface, which is very smooth, the charge constructing the electrostatic latent image will be destroyed due to too intimate a contact with the conductor. Moreover, under direct contact with the electrode, the effect of which is quite intense, an infinitely minute residual charge in the latent image will cause toner deposition to a considerable extent, which means a formation of undesirable background.

In case where the surface is sufficiently rough, the roller electrode will contact with the surface only at limited, raised microscopic regions; accordingly, such destruction of the image by leakage will not occur. Unfortunately, however, it is clear that such roughened surface cannot provide a print with highly smooth and uniform appearance.

In order to obtain a print of highest quality, it has been desirable to process an electrophotographic sheet with a very smooth surface without causing a direct contact'of an electrode with the surface or by employing a developing method in which the image destruction is effectively and ingeniously avoided upon direct contact with the electrode.

Another problem involved in the conventional devices such as shown in FIG. 1, the diameter of the pair rollers and the distance between the axes of the adjacent pairs cannot be made so small in order to drive all the pair rollers. In a developing device using roller electrodes, it is obvious that the effect of the development electrode is more complete with the use of small rollers in an increased numer and in a close distance therebetween.

According to the present invention, a developing apparatus is disclosed in which closely packed small diameter rollers are employed which are rotated in the same circumferential velocity as the advancing velocity of the insulating sheet to be developed. The apparatus of 'the present invention is characterized by that it is provided with nip rollers pairs in a number as small as possible, and smaller rollers placed in a close packing between these nip rollers and held apart from the surface on which the latent image is present with a close spacing and driven in the same circumferential velocity as the advancing velocity of the sheet.

The present invention will be explained more in detail with the illustrations of practical embodiments.

BRIEF DESCRIPTION OF THE INVENTION FIG. 1 is a longitudinal sectional view of a conventional electrophotographic liquid developing appara- FIG. 2 is a longitudinal sectional view of an embodiment according to the present invention.

FIGS. 3 and 4 are front views of the nip rollers used in the embodiment shown in FIG. 2.

FIG. 5 is a plane view showing the different arrangement of the rollers and endless belts.

FIG. 6 is a schematic sectional view of another embodiment according to the present invention.

FIG. 7 is a front view of the nip rollers used in the embodiment shown-in FIG. 7.

FIG. 8 is a front view of other nip rollers.

FIG. 9 is a front view of the developing electrode.

FIG. 10 is a schematic sectional view of the other embodiment according to the present invention.

DETAILED DESCRIPTION OF INVENTION In FIG. 2, l, 2 and 3 are supporting rollers having a smooth surface and a same diameter. They will be referred to as carrier rollers.

4, 5 and 6 designate suppressing or pressure rollers which are freely movable in the vertical direction having the same diameter as the carrier rollers l to 3. The suppressing rollers are on the carrier rollers. Each of these three pairs of rollers forms a nip construction. The diameter of these rollers, should be larger than 10 mm and up to about several hundred mm considering a smooth and constant speed rotation without rate fluctuation. The distances between the carrier rollers are much smaller than the length of the sheet to be developed. When one constitutes the rollers 4 to 6 with a metal or an electrically conductive material, they serve as development electrode. If the insulating layer has a very smooth surface on which an electrostatic latent image is formed, the direct contact with such being a problem, a roller covered with a thin insulating material may be employed.

7 and 8 designate two groups of finer rollers, which are finer than 4 to 6, closely arranged held by bearings. They are also movable in the vertical direction and placed on an endless belt 11 with which the rollers frictionally rotate. These finer rollers 7 and 8 will be called development electrode rollers. When the sheet advance horizontally, the rollers may be held by the bearings and on the belt by their own weight, thus they can shift in the vertical direction.

In all the following examples, the sheet advances horizontally; however, the advancing direction may be inclined relative to the horizon, and in an extreme case, may be vertical, whereby the rollers may be supported by springs having a suitable strength.

The thickness of the endless belt 11 is selected slightly greater than that of the sheet to be processed, while its width is arbitrary. The endless belts 11 are suspended between the carrier roller 1-3 at the both ends of the each roller and carried smoothly by rotation of these carrier rollers, and at the same time drive the electrode rollers 7 and 8 friction. The belts may be of any material which can satisfy the above mentioned functions.

The belts 11 must be thicker than the insulating sheet and, in order to drive the sheet by friction, the corresponding edge portions of the suppressing rollers are slightly indented as shown in FIG. 4. When the insulating sheet 100 is inserted the suppressing rollers 4 through 6 are forced to come up by the thickness of the sheet.

On the other hand, the finer rollers (electrode rollers) 7 and 8, having a uniform diameter, are rotated on the endless belts which are thicker than the sheet. Thus, they are not in direct contact with the surface of the sheet. In other words, the spacing between the finer rollers and the sheet surface is determined by the difference between thickness of the belt which works as spacer and that of the sheet.

It is a matter of course that the width of the sheet 100 should be smaller than the distance between the two endless belts parallelly suspended as shown in FIG. 3.

In FIGS. 2 through 4, the belts were suspended between the carrier rollers 1, 2 and 3: they may be suspended on the upper rollers 4 to 6. Such structure is shown in FIG. 6, which will be described more in detail later.

Drive of the rollers may be accomplished by rotating the rollers l, 2 or 3 in a constant circumferential speed by means of gear or chain. As a modification, each two adjacent rollers may be connected as shown in FIG. by endless belts whereby the belts serve as spacer as well as driving means.

In the device shown in FIG. 2, the developer liquid may be fed from above onto the sheet through nozzles 9, again collected in the tray provided beneath the driving station, and then led to a pump through the discharge exit 10. When the toner concentration of the developer is reduced or its performance deteriorates during usage, a concentrated developer may be added or the whole volume of the liquid may be replaced by a fresh volume.

Though in general the endless belt 11 thicker than the sheet 100 (it is preferable as described above) will prevent the direct contact of the electrode rollers with the latent image bearing surface of the sheet, it is not necessary and sufficient conditions for ensuring perfect elimination of such contact.

Even if the endless belt is thinner than the sheet, there are cases where the direct contact does not occur when other suitable conditions are satisfied. When the belt is held in a high tension or the belt is formed of a highly elastic material, the electrode rollers on the belt will lie in a single plane between the carrier rollers l to 3.

On the other hand, when the developer liquid is supplied from above onto the surface of the sheet 100, the sheet will show a slight bend between the carrier rollers. In the case where the extent of bending is substantially equal for the belt and the sheet, the spacing between the electrode roller and the sheet surface will be determined primarily by their thickness difference. When the belt 11 bends more than the sheet 100, the spacing will become smaller than the thickness difference and in some cases the sheet surface will come into contact with the electrode rollers. If the sheet bends to a greater extent than the belt 11 does, the spacing will become larger and even a belt thinner than the sheet will cause no direct contact between the sheet and electrode rollers.

In the apparatus shown in FIG. 2, as will be selfevident from the relative positions of the carrier roller, the suppressing roller, the endless belt and the sheet (refer to FIG. 4), the nominal spacing (thickness difference between the belt and the sheet in the case the extent of bending is equal for the belt and the sheet) will naturally depend on the thickness of the sheet. In other words, the spacing will vary due to the variety of the variety of the thickness of the sheets.

An apparatus is shown in FIG. 6 which is free from such dependence; in this embodiment an endless belt is suspended between suppressing rollers instead of carrier rollers. The edge portions of the suppressing rollers around which the endless belts are wound are made indented as shown in FIG. 7. The difference of the radius between the middle and the edge portions of the suppressing rollers is the nominal spacing. In this apparatus, no change of spacingoccurs with sheets of different thickness, since the electrode rollers are held on the endless belts. In FIG. 7 is illustrated the front view of the apparatus shown in FIG. 6 wherein the sheet is nipped between the carrier roller 81 and the suppressing roller 84.

In the above embodiments the carrier rollers were driven by an outer means, while the suppressing rollers held movable in the vertical direction were rotated frictionally with the carrier rollers. However, suppressing rollers may be held rigid by bearings and driven by an outer driving means while the carrier rollers are pushed upwardly by the aid of spring and rotated frictionally by the suppressing rollers.

The diameters of carrier and suppressing rollers may be different from each other, and may preferably fall between 10 mm to several 10 mmto realize contact area with the sheet enough to insurestable transport of the sheet. The distance between the axes of the adjacent rollers must be smaller than the length of the sheet to be processed measured alongthe advancing direction.

In the illustrated examples, only three carrier rollers were provided, but, more or less numbers of rollers may be used.

Suitable material for the carrier roller include metal, plastic, rubber, and many other ones. A smooth surface is desirable to avoid smudging of the back surface of the sheet.

The effect of the electrode rollers as development electrode will increase as more number of rollers with smaller diameter are used.

Too fine rollers, however, will suffer distortion or fall to rotate smoothly whereby they will slip or scrape the developed toner image on the sheet, and a relative movement will take place between the developer liquid and the sheet surface which will cause streaks in the developed toner image. Thus, from practical point of view, rollers with l to 10 mm diameter are preferred since they will scarcely show too much distortion and will rotate smoothly by the friction with the endless belts.

The mutual distance between the electrode rollers would be as small as possible. The adjacent ones may be in light contact with each other as long as smooth rotation is not hindered. Preferred range may be 0.1 to

1.0 mm. They may be made of metal preferably with a smooth surface. Suitable examples include polished stainless steel, carbon steel, brass, duralmin, etc. Provided that the roller can effectively attract electric lines of force from an electrostatic latent image, any structure of the roller may be permitted. For example, a thin insulating surface layer may be provided on a conductive core, or a metal roller may be surface treated to form an oxide surface layer thereon. Such surface layer works to prevent the destruction of an electrostatic latent image by leakage when it comes into contact with the latent image. Five electrode rollers are shown in FIG. 6, while the number may be more or less.

In all the practical examples, the latent image bearing surface is not in contact with fine electrode rollers but only with suppressing rollers. In case where the supressing rollers work as development electrode which con tacting with the surface bearing latent image, a negligible small residual potential at background area in the latent image will be sharply detected and attract undesirable toner, as has been described in the first part of the disclosure. However, according to the essential feature of the present invention, the contribution from the finer rollers far surpasses that from small number of the suppressing roller and thus such defect is greatly reduced.

Now another example will be shown in which even suppressing rollers never come in contact with the surface of the sheet to be developed during development. FIG. 8 is a front view of such apparatus which has substantially a similar configuration as that shown in FIG. 6. Another pair of narrow endless belts I01 and 102 is suspended on the suppressing rollers 104 and grooves 103 are provided to hold the belts near the both ends of the suppressing rollers. The clearance between the sheet surface and the suppressing roller becomeequal to the thickness of the belt 101 minus the depth of the groove 103. v

In this structure, the suppressing roller 104 may preferably be made of conductive material to function as development electrode. I

' In place of fine electrode rollers with a uniform diameter held on an endless belt asshown in FIG. 6, those having scraped edge portions as shown in FIG. 9 may also be employed. With such electrode rollers, one can adjust the spacing between the roller and the sheet surface, and advantageously regulate the movement (shift) of the roller alongs its length. With the use of suppressing rollers provided with endless belts the relative arrangement of sheet and rollers becomes such as shown in FIG. 8, in which, sheet I00 is held at the both edges by endless belts 101 and 102 and transported by the rotation of the carrier roller 105. Accordingly the suppressing roller 104 is not indirect contact with the sheet. in such arrangement, the distance between the adjacent suppressing rollers may be larger than the length of the sheet. FIG. 10 illustrates another embodiment of the invention, in which an endless belt 131 is suspended between a pair of carrier rollers. This belt 131 may be wide enough to support the whole width of a sheet to be processed, or similar to 101 or 102 in FIG. 8 provided at the both edges of the carrier rollers. in the embodiment shown in FIG. 3 to FIG. 10, there were not shown means to supply developer, and reservoir for developer which are essentially necessary and only abbreviated.

What we claim is:

1. An electrophotographic developing apparatus employing a liquid developer for developing an electrostatic latent image on an insulating sheet, said apparatus comprising;

l. at least two pairs of nip rollers, each pair comprising a first roller disposed on one side of said insulating sheet and a second roller disposed adjacent said first roller and on the opposite side of said insulating sheet where the rollers nip and transport said insulating sheet and where successive pairs of rollers are disposed along the direction of movement of said sheet,

2. at least one pair of endless belts suspended between selected nip rollers at the end portions thereof so that one of said pair of endless belts is disposed about the end portions. of said selected rollers and the other of said pair of endless belts is disposed about the opposite ends of said selected rollers, said selected rollers being disposed along the direction of movement and one side of said insulating sheet,

3. a plurality of development electrode rollers disposed'between each adjacent pair of first rollers and on the same side of said insulating sheet as each of said first rollers and having smaller diameters than said nip rollers, the end portions of said development electrode rollers being disposed on said endless belts, and i 4. means for supplying said developer liquid onto the surface of the sheetbearing the electrostatic latent image.

2. Apparatus as in claim 1 where the diameters of said end portions of said electrode development rollers are smaller than the respective middle portions thereof to minimize movement of said latter rollers along the length thereof and to set the spacing between said latter rollers and the insulating sheet.

3. Apparatus as in claim 1 where the diameters of the end portions of said first rollers are smaller than the respective middle portions thereof.

4. Apparatus as in claim 1 where as said am .01...

is electrically conductive and has an electrically insulative overcoating thereon.

5. Apparatus as in claim 1 where each said development electrode roller is electrically conductive and has an electrically insulstive overcoating thereon.

6. Apparatus as in claim 1 where the diameter of each of said nip rollers is greater than about 10 millimeters while the development electrode rollers have a diameter range from about 1 millimeter to 10 millimeters.

7. Apparatus as in claim 6 where distance range between adjacent development electrode rollers is about 0.1 to 1.0 millimeter. V I

8. Apparatus as in claim 1 where each pair of nip rollers adjacent along the direction of travel of the insulating sheet have suspended therebetween a pair of said endless belts at the respective ends thereof.

9.Apparatus as in claim 1 where said development electrode rollers are mounted outside of the loop formed by each of the endless belts.

10. Apparatus as in claim 9 where the diameter of each said development electrode roller is constant over the length thereof and where the thickness of each of said endless belts is greater than that of said insulating sheet whereby contact between said electrode development rollers and said insulating sheet is minimized, the

nominal distance between said development electrode rollers and said insulating sheet being the difference in the thickness of said endless belts and said insulating sheet.

11. Apparatus as in claim 9 where said endless belt is suspended between at least two of said second rollers.

12. Apparatus as in claim 9 where th width of said insulating sheet is less than the distance between the endless belts.

13. Apparatus as in claim 1 where the direction of movement of said insulating sheet is substantially horizontal.

14. Apparatus as in claim 1 where said development electrode rollers are mounted inside of the loop formed by each of said endless belts.

15. Apparatus as in claim 14 where the diameters of the end portions of said first rollers are smaller than the respective middle portions thereof and said endless belts are suspended between said first rollers, the nominal distance between said development electrode rollers and said insulating sheet being the difference in the radii of the middle and end portions of said first rollers whereby contact between said development electrode rollers and said insulating sheet is minimized and said nominal spacing is independent of the thickness of said insulating sheet.

16. Apparatus as in claim 15 where the width of said insulating sheet is greater than the distance between said pair of endless belts, said insulating sheet being disposed between said endless belts and said first rollers so that the clearance between said first rollers and said insulating sheet is equal to the difference between the thickness of the endless belts and the depth of the indentations at the respective ends of said first rollers.

17. Apparatus as in claim 16 where the indentations at the respective ends of said first rollers are grooves, said end belts being disposed within said grooves.

18. Apparatus as in claim 16 where the distance between adjacent pairs of first rollers is greater than the length of said insulating sheet.

19. Apparatus as in claim 16 where at least one further endless belt is suspended between said second rollers, the width of said further belt being approximately as wide as said insulating sheet.

20. Apparatus as in claim16 where at least one pair of further endless belts are suspended between said second rollers at the respective ends thereof.

' 0 l l I 

1. An electrophotographic developing apparatus employing a liquid developer for developing an electrostatic latent image on an insulating sheet, said apparatus comprising;
 1. at least two pairs of nip rollers, each pair comprising a first roller disposed on one side of said insulating sheet and a second roller disposed adjacent said first roller and on the opposite side of said insulating sheet where the rollers nip and transport said insulating sheet and where successive pairs of rollers are disposed along the direction of movement of said sheet,
 2. at least one pair of endless belts suspended between selected nip rollers at the end portions thereof so that one of said pair of endless belts is disposed about the end portions of said selected rollers and the other of said pair of endless belts is disposed about the opposite ends of said selected rollers, said selected rollers being disposed along the direction of movement and one side of said insulating sheet,
 3. a plurality of development electrode rollers disposed between each adjacent pair of first rollers and on the same side of said insulating sheet as each of said first rollers and having smaller diameters than said nip rolLers, the end portions of said development electrode rollers being disposed on said endless belts, and
 4. means for supplying said developer liquid onto the surface of the sheet bearing the electrostatic latent image.
 2. at least one pair of endless belts suspended between selected nip rollers at the end portions thereof so that one of said pair of endless belts is disposed about the end portions of said selected rollers and the other of said pair of endless belts is disposed about the opposite ends of said selected rollers, said selected rollers being disposed along the direction of movement and one side of said insulating sheet,
 2. Apparatus as in claim 1 where the diameters of said end portions of said electrode development rollers are smaller than the respective middle portions thereof to minimize movement of said latter rollers along the length thereof and to set the spacing between said latter rollers and the insulating sheet.
 3. Apparatus as in claim 1 where the diameters of the end portions of said first rollers are smaller than the respective middle portions thereof.
 3. a plurality of development electrode rollers disposed between each adjacent pair of first rollers and on the same side of said insulating sheet as each of said first rollers and having smaller diameters than said nip rolLers, the end portions of said development electrode rollers being disposed on said endless belts, and
 4. Apparatus as in claim 1 where each said first roller is electrically conductive and has an electrically insulative overcoating thereon.
 4. means for supplying said developer liquid onto the surface of the sheet bearing the electrostatic latent image.
 5. Apparatus as in claim 1 where each said development electrode roller is electrically conductive and has an electrically insulative overcoating thereon.
 6. Apparatus as in claim 1 where the diameter of each of said nip rollers is greater than about 10 millimeters while the development electrode rollers have a diameter range from about 1 millimeter to 10 millimeters.
 7. Apparatus as in claim 6 where distance range between adjacent development electrode rollers is about 0.1 to 1.0 millimeter.
 8. Apparatus as in claim 1 where each pair of nip rollers adjacent along the direction of travel of the insulating sheet have suspended therebetween a pair of said endless belts at the respective ends thereof.
 9. Apparatus as in claim 1 where said development electrode rollers are mounted outside of the loop formed by each of the endless belts.
 10. Apparatus as in claim 9 where the diameter of each said development electrode roller is constant over the length thereof and where the thickness of each of said endless belts is greater than that of said insulating sheet whereby contact between said electrode development rollers and said insulating sheet is minimized, the nominal distance between said development electrode rollers and said insulating sheet being the difference in the thickness of said endless belts and said insulating sheet.
 11. Apparatus as in claim 9 where said endless belt is suspended between at least two of said second rollers.
 12. Apparatus as in claim 9 where th width of said insulating sheet is less than the distance between the endless belts.
 13. Apparatus as in claim 1 where the direction of movement of said insulating sheet is substantially horizontal.
 14. Apparatus as in claim 1 where said development electrode rollers are mounted inside of the loop formed by each of said endless belts.
 15. Apparatus as in claim 14 where the diameters of the end portions of said first rollers are smaller than the respective middle portions thereof and said endless belts are suspended between said first rollers, the nominal distance between said development electrode rollers and said insulating sheet being the difference in the radii of the middle and end portions of said first rollers whereby contact between said development electrode rollers and said insulating sheet is minimized and said nominal spacing is independent of the thickness of said insulating sheet.
 16. Apparatus as in claim 15 where the width of said insulating sheet is greater than the distance between said pair of endless belts, said insulating sheet being disposed between said endless belts and said first rollers so that the clearance between said first rollers and said insulating sheet is equal to the difference between the thickness of the endless belts and the depth of the indentations at the respective ends of said first rollers.
 17. Apparatus as in claim 16 where the indentations at the respective ends of said first rollers are grooves, said end belts being disposed within said grooves.
 18. Apparatus as in claim 16 where the distance between adjacent pairs of first rollers is greater than the length of said insulating sheet.
 19. Apparatus as in claim 16 where at least one further endless belt is suspended between said second rollers, the width of said further belt being approximately as wide as said insulating sheet.
 20. Apparatus as in claim 16 where at least one pair of further endless belts are suspended between said second rollers at the respective ends thereof. 